Given

Speed of sound (u) = 342 m/s

Time taken for hearing the echo (t) = 6 s

Now

⇒

⇒ Distance travelled by the sound = 342 ×6 = 2052 m.

In 6s, sound has to travel twice the distance between the source and reflecting surface. Therefore, the distance of the reflecting surface from the source = = 1026 m

Distance of reflecting surface = 1026 m